Modified catalyst supports

ABSTRACT

The invention covers a supported catalyst system prepared according to a process comprising the following step:
         i). impregnating a silica-containing catalyst support having a specific surface area of from 150 m 2 /g to 800 m 2 /g, preferably 280 m 2 /g to 600 m 2 /g, with one or more titanium compounds of the general formula selected from R n Ti(OR′) m  and (RO) n Ti(OR′) m , wherein R and R′ are the same or different and are selected from hydrocarbyl groups containing from 1 to 12 carbon and halogens, and wherein n is 0 to 4, m is 0 to 4 and m+n equals 4, to form a titanated silica-containing catalyst support having a Ti content of at least 0.1 wt % based on the weight of the Ti-impregnated catalyst support
 
wherein the supported catalyst system further comprises an alumoxane and a metallocene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/807,559, filed Apr. 15, 2013, which claims the benefit ofPCT/EP2011/061146, filed Jul. 1, 2011, which claims priority from EP10168151.8, filed Jul. 1, 2010 and EP 10172640.4 filed Aug. 12, 2010,which are herein incorporated by reference in their entireties for allpurposes.

FIELD OF THE INVENTION

The invention relates to a process for preparing modified catalystsupports, in particular catalyst supports suitable for metallocenecatalyst systems.

The invention also relates to the support obtained according to thisprocess, as well as a catalyst system comprising such a support and theolefin polymerisation process using such a support.

BACKGROUND OF THE INVENTION

Metallocene catalyst systems are extensively used in a variety ofpolymerisation systems, including the polymerisation of olefins.Generally, in order to obtain the highest activity from metallocenecatalysts, it has been necessary to use them with an organoaluminoxaneactivating agent, such as methylaluminoxane (MAO). This resultingcatalyst system is generally referred to as a homogenous catalyst systemsince at least part of the metallocene or the organoaluminoxane is insolution in the polymerisation media. These homogenous catalyst systemshave the disadvantage that when they are used under slurrypolymerisation conditions, they produce polymers which stick to thereactor walls during the polymerisation process (generally referred toas “fouling”) and/or polymers having small particle size and low bulkdensity which limit their commercial utility.

Various methods have been proposed in an effort to overcome thedisadvantages of the homogenous metallocene catalyst systems. Typically,these procedures have involved the prepolymerisation of the metallocenealuminoxane catalyst system and/or supporting the catalyst systemcomponents on a porous carrier (also known as a “particulate solid” or“support”). The porous carrier is usually a silica-containing support.

Another important consideration in the development of metallocenecatalysts is the yield of solid polymer that is obtained by employing agiven quantity of catalyst in a given amount of time. This is known asthe “activity” of the catalyst. There is an ongoing search formetallocene catalysts and techniques for preparing such catalysts whichgive improved activity for the polymerisation of olefins. An improvedactivity means that less catalyst needs to be used to polymerise moreolefins, thereby reducing the costs considerably, since metallocenes aremore expensive than Ziegler-Natta and chromium catalysts.

Several attempts have been made to titanate silica supports for use inmetallocene catalysed ethylene polymerisations. Jongsomjit et al.(Molecules 2005, 10, 672, Ind. Eng. Chem. Res. 2005, 44, 9059 andCatalysis Letters Vol. 100, Nos. 3-4, April 2005) discloses thetitanation of silicas for zirconocene catalysed ethylene polymerisation,wherein the support is prepared according to Conway et al. (J. Chem.Soc., Faraday Trans. J, 1989, 85(1), 71-78) using mixed supports oftitania and silica mixed-oxide supports. The increase in activity withsuch a support is only of 25%, because the titania is presentpredominantly in its anatase form i.e. a crystalline form. Underpolymerisation conditions, little morphological control can be obtainedwith such a support. It is particularly difficult to use industrially,since the porous volume, bulk density and particle size of both thesilica and titania need to be similar in order to avoid decantation ofone with respect to the other. In addition, the interaction of the Tiwith the actives sites is not optimized.

Thus, a new catalyst support is needed for metallocene catalysts whichcan induce improved activity of the metallocene catalyst system,particularly under industrial conditions.

An object of the present invention is to provide a new catalyst supportfor metallocene catalysts to increase their activity.

Furthermore, it is an object of the present invention to provide a newmethod for polymerising olefins, preferably ethylene and propylene,using a new supported metallocene catalyst system.

SUMMARY OF THE INVENTION

At least one of the objects is solved by the present invention.

A supported catalyst system is provided obtainable by a processcomprising the following step:

-   -   i) titanating a silica-containing catalyst support having a        specific surface area of from 150 m²/g to 800 m²/g, preferably        280 to 600 m²/g, more preferably 280 m²/g to 400 m²/g, by        impregnating the support with a titanium compound of the general        formula selected from R_(n)Ti(OR′)_(m) and (RO)_(n)Ti(OR′)_(m),        wherein R and R′ are the same or different and are selected from        hydrocarbyl groups containing from 1 to 12 carbon and halogens,        preferably chlorine and fluorine, and wherein n is 0 to 4, m is        0 to 4 and m+n equals 4, to form a titanated silica-containing        catalyst support having a Ti wt % of at least 0.1 wt %

wherein the supported catalyst system further comprises an alumoxane anda metallocene.

The supported catalyst system may further comprise the following stepafter step (i):

-   -   ii) treating the titanated support with a catalyst activating        agent, preferably an alumoxane.

The process may further comprise the following step during or after step(ii):

-   -   iii) treating the titanated support with a metallocene.

There is also provided a process for preparing a polyethylene comprisingthe step of polymerising olefins, preferably ethylene or propylene, inthe presence of a supported catalyst system according to the invention,preferably in the gas phase or in the slurry phase. Optionally, in thecase of ethylene polymerization, the ethylene is copolymerised with oneor more alpha-olefin comonomers selected from C3 to C12 alpha-olefins.Optionally, in the case of propylene polymerization, the propylene iscopolymerized with one or more alpha olefin comonomers selected fromethylene, and C4 to C12 alpha-olefins.

The polyethylene obtainable by the process of the invention is also newand inventive and has surprising rheological properties.

Surprisingly the catalyst support according to the invention improvesthe activity of the metallocene deposited thereon, since the interactionof the Ti within the support is optimized. It is believed, without beingbound to theory, that the titanation step according to the invention byimpregnation rather than simple physical mixing of oxides, causes thetitanium compound to form Si—O—Ti—OH on the surface of the pores withinthe silica support even before alumoxane (e.g. MAO) addition.Furthermore, once an alumoxane is added, its interaction with TiOH andSiOH is optimized. The electronic effect of the specific Ti distributionon the catalyst grain surface increases the metallocene catalystsystem's activity as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a comparison of the catalytic activities of themetallocene catalyst system comprising the titanium compound addedaccording to the invention containing a titanium content of 2 wt % and 4wt % according to the invention with the catalytic activities ofmetallocene catalyst systems not containing any titanium.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for preparing asilica-containing catalyst support, for preparing the catalyst systemprepared with said support and for the production of polyolefins withsaid catalyst system. The support according to the invention isparticularly suitable for metallocene catalyst polymerisations, since itincreases the activity of the metallocene catalyst system considerably.

Suitable supports used in this invention are silica-based and compriseamorphous silica having a surface area of at least 150 m²/g, preferablyof at least 200 m²/g, more preferably of at least 280 m²/g, and at most800 m²/g, preferably to at most 600 m²/g, more preferably to at most 400m²/g and more preferably to at most 380 m²/g. The specific surface areais measured by N₂ adsorption using the well-known BET technique.

Silica-containing supports contain at least 20, 40, or 50% by weight ofamorphous silica. The silica-containing support may also contain one ormore of alumina, magnesia, zirconia and the like.

Preferably the support is a silica support i.e. essentially 100% byweight of silica, or a silica-alumina support. In the case ofsilica-alumina supports, the support preferably comprises at most 15% byweight of alumina.

In general, the supports advantageously have a pore volume of 1 cm³/g to3 cm³/g. Supports with a pore volume of 1.3-2.0 cm³/g are preferred.Pore volume is measured by N₂ desorption using the BJH method for poreswith a diameter of less than 1000 Å. Supports with too small a porositymay result in a loss of melt index potential and in lower activity.Supports with a pore volume of over 2.5 cm³/g or even with a pore volumeof over 2.0 cm³/g are less desirable because they may require specialexpensive preparation steps (e.g. azeotropic drying) during theirsynthesis. In addition, because they are usually more sensitive toattrition during catalyst handling, activation or use in polymerisation,these supports often lead to more polymer fines production, which isdetrimental in an industrial process.

The silica-containing support can be prepared by various knowntechniques such as but not limited to gelification, precipitation and/orspray-drying. Usually, the particle size D50 is from 5 μm, preferablyfrom 30 μm and more preferably from 35 μm, up to 150 μm, preferably upto 100 μm and most preferably up to 70 μm. D50 is defined as theparticle diameter, where 50 wt-% of particles have a smaller diameterand 50 wt-% of particles have a larger diameter. Particle size D90 is upto 200 μm, preferably up to 150 μm, most preferably up to 110 μm. D90 isdefined as the particle diameter where 90 wt-% of particles have asmaller diameter and 10 wt-% of particles have a larger diameter.Particle size D10 is at least 2 μm, preferably at least 5 μm. D10 isdefined as the particle diameter where 10 wt-% of particles have asmaller diameter and 90 wt-% of particles have a larger diameter.Particle size distribution is determined using light diffractiongranulometry, for example, using the Malvern Mastersizer 2000. Theparticle morphology is preferably microspheroidal to favour fluidisationand to reduce attrition.

The silica-containing support is loaded with one or more titaniumcompounds selected from R_(n)Ti(OR′)_(m) and (RO)_(n)Ti(OR′)_(m),wherein R and R′ are the same or different and are selected fromhydrocarbyl groups containing from 1 to 12 carbon and halogens,preferably chlorine and fluorine, and wherein n is 0 to 4, m is 0 to 4and m+n equals 4. From the halogens any element from Group VIIa can beselected. The titanium compound is preferably selected from the groupconsisting of tetraalkoxides of titanium having the general formulaTi(OR′)₄ wherein each R is the same or different and can be an alkyl orcycloalkyl group each having from 3 to 5 carbon atoms, and mixturesthereof.

The titanium compound(s) with which the support is impregnated is morepreferably selected from alkyl titanates, preferably selected from e.g.Ti(OC₄H₉)₄, Ti(OC₃H₇)₄. More preferably a mixture of alkyl titanates areused e.g. a mixture of Ti(OC₄H₉)₄ and Ti(OC₃H₇)₄. Most preferably themixture has a weight ratio of 20/80 of Ti(OC₄H₉)₄ to Ti(OC₃H₇)₄. Theimpregnation of the support with akyl titanate is preferably performedby introducing the titanium compound(s) in a suspension in a diluentsuch as an organic solvent e.g. hexane or iso-hexane, or dissolved in anaqueous solvent. The suspension is preferably added drop wise to thesupport. The suspension is then mixed preferably for at least 1 hour,more preferably at least 2 hours.

The total amount of titanium compound(s) used to impregnated iscalculated in order to obtain the required titanium content in theresultant catalyst support and preferably the progressive flow rate ofthe titanium compound is adjusted in order to provide a titanationreaction period of 0.5 to 2 hours. The resulting impregnated support hasa Ti content of from 0.1 to 60 wt %, preferably 0.1 to 25 wt %, morepreferably 0.5 to 15 wt %, most preferably 1 to 10 wt %.

The supported catalyst system obtainable by this process may furthercomprise the step:

-   -   drying the Ti-impregnated catalyst support prior to the addition        of alumoxane and metallocene.

The support is dried after titanation, preferably by heating to atemperature of from 100° C., preferably of at least 250° C., morepreferably of at least 270° C. This step generally lasts for at least 1hour, more preferably at least 2 hours, most preferably at least 4hours. The drying can take place in an atmosphere of dry and inert gasand/or air, preferably nitrogen. The drying may be carried out in afluidised bed.

After impregnation and optional drying the titanated catalyst supportcan be stored under a dry and inert atmosphere, for example, nitrogen,at ambient temperature.

The details and embodiments mentioned above in connection with theprocess for manufacturing the catalyst support also apply with respectto the preparation of the supported catalyst system according to thepresent invention.

The supported catalyst system obtainable by the process of the inventionmay further comprise the step:

-   -   adding alumoxane to the Ti-impregnated catalyst support prior to        or during the addition of metallocene.

The catalyst support is treated with a catalyst activating agent afterimpregnation. In a preferred embodiment, alumoxane or a mixture ofalumoxanes are used as an activating agent for the metallocene, but anyother activating agent known in the art can be used e.g. boranecompounds. The alumoxane can be used in conjunction with the metallocenein order to improve the activity of the catalyst system during thepolymerisation reaction. As used herein, the term alumoxane is usedinterchangeably with aluminoxane and refers to a substance, which iscapable of activating the metallocene.

Alumoxanes used in accordance with the present invention compriseoligomeric linear and/or cyclic alkyl alumoxanes. In an embodiment, theinvention provides a process wherein said alumoxane has formula (III) or(IV)R—(Al(R)—O)_(x)—AlR₂  (III) for oligomeric, linear alumoxanes; or(—Al(R)—O—)_(y)  (IV) for oligomeric, cyclic alumoxanes

-   -   wherein x is 1-40, and preferably 10-20;    -   wherein y is 3-40, and preferably 3-20; and    -   wherein each R is independently selected from a C₁-C₈ alkyl, and        preferably is methyl.

In a preferred embodiment, the alumoxane is methylalumoxane (MAO).Generally, in the preparation of alumoxanes from, for example, aluminumtrimethyl and water, a mixture of linear and cyclic compounds isobtained. Methods for manufacturing alumoxane are known in the art andwill therefore not be disclosed in detail herein.

The treatment of the catalyst support with the alumoxane can be carriedout according to any known method known by the person skilled in theart. Advantageously, the alumoxane, preferably MAO, is mixed in an inertdiluent/solvent, preferably toluene, with the catalyst support.Alumoxane deposition preferably occurs at a temperature between 60° C.to 120° C., more preferably 80° C. to 120° C., most preferably 100 to120° C. The amount of MAO is calculated to reach the desired aluminiumloading.

The catalyst support is treated with a metallocene either duringtreatment with the catalyst activating agent (1-pot method) orthereafter. Any metallocene known in the art can be applied, including amixture of different metallocenes. As used herein, the term“metallocene” refers to a transition metal complex with a coordinatedstructure, consisting of a metal atom bonded to one or more ligands. Themetallocene are used according to the invention is preferably chosenfrom formula (I) or (II):(Ar)₂MQ₂  (I); orR″(Ar)₂MQ₂  (II)

-   -   wherein the metallocenes according to formula (I) are        non-bridged metallocenes and the metallocenes according to        formula (II) are bridged metallocenes;    -   wherein said metallocene according to formula (I) or (II) has        two Ar bound to M which can be the same or different from each        other;    -   wherein Ar is an aromatic ring, group or moiety and wherein each        Ar is independently selected from the group consisting of        cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl,        wherein each of said groups may be optionally substituted with        one or more substituents each independently selected from the        group consisting of hydrogen, halogen and a hydrocarbyl having 1        to 20 carbon atoms and wherein said hydrocarbyl optionally        contains one or more atoms selected from the group comprising B,        Si, S, O, F and P;    -   wherein M is a transition metal M selected from the group        consisting of titanium, zirconium, hafnium and vanadium; and        preferably is zirconium;    -   wherein each Q is independently selected from the group        consisting of halogen; a hydrocarboxy having 1 to 20 carbon        atoms; and a hydrocarbyl having 1 to 20 carbon atoms and wherein        said hydrocarbyl optionally contains one or more atoms selected        from the group comprising B, Si, S, O, F and P; and    -   wherein R″ is a divalent group or moiety bridging the two Ar        groups and selected from the group consisting of a C₁-C₂₀        alkylene, a germanium, a silicon, a siloxane, an alkylphosphine        and an amine, and wherein said R″ is optionally substituted with        one or more substituents each independently selected from the        group comprising a hydrocarbyl having 1 to 20 carbon atoms and        wherein said hydrocarbyl optionally contains one or more atoms        selected from the group comprising B, Si, S, O, F and P.

The term “hydrocarbyl having 1 to 20 carbon atoms” as used herein isintended to refer to a moiety selected from the group comprising alinear or branched C₁-C₂₀ alkyl; C₃-C₂₀ cycloalkyl; C₆-C₂₀ aryl; C₇-C₂₀alkylaryl and C₇-C₂₀ arylalkyl, or any combinations thereof.

Exemplary hydrocarbyl groups are methyl, ethyl, propyl, butyl, amyl,isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl,2-ethylhexyl, and phenyl.

Exemplary halogen atoms include chlorine, bromine, fluorine and iodineand of these halogen atoms, chlorine is preferred.

Exemplary hydrocarboxy groups are methoxy, ethoxy, propoxy, butoxy, andamyloxy.

In accordance with the present invention, a process is provided whereinethylene monomer is polymerised in the presence of a bridged ornon-bridged metallocene. “Bridged metallocenes” as used herein, aremetallocenes in which the two aromatic transition metal ligands, denotedas Ar in formula (I) and (II) are covalently linked or connected bymeans of a structural bridge. Such a structural bridge, denoted as R″ informula (I) and (II) imparts stereorigidity on the metallocene, i.e. thefree movement of the metal ligands is restricted. According to theinvention, the bridged metallocene consists of a meso or racemicstereoisomer.

The two Ar can be the same or different. In a preferred embodiment thetwo Ar are both indenyl or both tetrahydroindenyl wherein each of saidgroups may be optionally substituted with one or more substituents eachindependently selected from the group consisting of hydrogen, halogenand a hydrocarbyl having 1 to 20 carbon atoms and wherein saidhydrocarbyl optionally contains one or more atoms selected from thegroup comprising B, Si, S, O, F and P. If substituted, both Ar arepreferably identically substituted. However, in a preferred embodiment,both Ar are unsubstituted.

In a preferred embodiment, the metallocene used in a process accordingto the invention is represented by formula (I) or (II) as given above,

-   -   wherein Ar is as defined above, and wherein both Ar are the same        and are selected from the group consisting of cyclopentadienyl,        indenyl, tetrahydroindenyl and fluorenyl, wherein each of said        groups may be optionally substituted with one or more        substituents each independently selected from the group        consisting of halogen and a hydrocarbyl having 1 to 20 carbon        atoms as defined herein;    -   wherein M is as defined above, and preferably is zirconium,    -   wherein Q is as defined above, and preferably both Q are the        same and are selected from the group consisting of chloride,        fluoride and methyl, and preferably are chloride; and    -   and wherein R″ when present, is as defined above and preferably        is selected from the group consisting of a C₁-C₂₀ alkylene, and        a silicon, and wherein said R″ is optionally substituted with        one or more substituents each independently selected from the        group comprising a halogen, hydrosilyl, hydrocarbyl having 1 to        20 carbon atoms as defined herein.

In another preferred embodiment, the metallocene used in a processaccording to the invention is represented by formula (I) or (II) asgiven above,

-   -   wherein Ar is as defined above, and wherein both Ar are        different and are selected from the group consisting of        cyclopentadienyl, indenyl, tetrahydroindenyl and fluorenyl,        wherein each of said groups may be optionally substituted with        one or more substituents each independently selected from the        group consisting of, halogen and a hydrocarbyl having 1 to 20        carbon atoms as defined herein;    -   wherein M is as defined above, and preferably is zirconium,    -   wherein Q is as defined above, and preferably both Q are the        same and are selected from the group consisting of chloride,        fluoride and methyl, and preferably are chloride; and    -   and wherein R″ when present is as defined above and preferably        is selected from the group consisting of a C₁-C₂₀ alkylene, and        a silicon, and wherein said R″ is optionally substituted with        one or more substituents each independently selected from the        group comprising a hydrocarbyl having 1 to 20 carbon atoms as        defined herein.

In an embodiment, the invention provides a process wherein saidmetallocene is an unbridged metallocene.

In a preferred embodiment, the invention provides a process wherein saidmetallocene is an unbridged metallocene selected from the groupcomprising bis(iso-butylcyclopentadienyl) zirconium dichloride,bis(pentamethylcyclopentadienyl) zirconium dichloride,bis(tetrahydroindenyl) zirconium dichloride, bis(indenyl) zirconiumdichloride, bis(1,3-dimethylcyclopentadienyl) zirconium dichloride,bis(methylcyclopentadienyl) zirconium dichloride,bis(n-butylcyclopentadienyl) zirconium dichloride, andbis(cyclopentadienyl) zirconium dichloride; and preferably selected fromthe group comprising bis(cyclopentadienyl) zirconium dichloride,bis(tetrahydroindenyl) zirconium dichloride, bis(indenyl) zirconiumdichloride, and bis(1-methyl-3-butyl-cyclopentadienyl)zirconiumdichloride.

In another embodiment, the invention provides a process wherein saidmetallocene is a bridged metallocene.

In a preferred embodiment, the invention provides a process wherein saidmetallocene is a bridged metallocene selected from the group comprisingethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride,ethylenebis(1-indenyl) zirconium dichloride, dimethylsilylenebis(2-methyl-4-phenyl-inden-1-yl) zirconium dichloride, dimethylsilylenebis(2-methyl-1H-cyclopenta[a]naphthalen-3-yl) zirconium dichloride,cyclohexylmethylsilylene bis[4-(4-tert-butylphenyl)-2-methyl-inden-1-yl]zirconium dichloride, dimethylsilylenebis[4-(4-tert-butylphenyl)-2-(cyclohexylmethyl)inden-1-yl] zirconiumdichloride. Ethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconiumdichloride is particularly preferred.

In another preferred embodiment, the invention provides a processwherein said metallocene is a bridged metallocene selected from thegroup comprising diphenylmethylene (3-t-butyl-5-methyl-cyclopentadienyl)(4,6-di-t-butyl-fluorenyl) zirconium dichloride,di-p-chlorophenylmethylene (3-t-butyl-5-methyl-cyclopentadienyl)(4,6-di-t-butyl-fluorenyl) zirconium dichloride, diphenylmethylene(cyclopentadienyl)(fluoren-9-yl) zirconium dichloride, dimethylmethylene(cyclopentadienyl)(2,7-ditert-butyl-fluoren-9-yl) zirconium dichloride,dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](fluoren-9-yl) zirconiumdichloride, diphenylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](2,7-ditert-butyl-fluoren-9-yl) zirconium dichloride, dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](3,6-ditert-butyl-fluoren-9-yl) zirconium dichloride dimethylmethylene(cyclopentadienyl)(fluoren-9-yl) zirconium dichloride anddibenzylmethylene(2,7-diphenyl-3,6-di-tert-butyl-fluoren-9-yl)(cyclopentadienyl)zirconiumdichloride.

The support is treated with the metallocene, advantageously by mixingthe desired metallocene(s) with the MAO-modified support. Preferablymixing occurs at room temperature for a duration of at least 15 min,preferably at least 1 hour, more preferably at least 2 hours.

In a particular embodiment, the invention provides a process wherein themolar ratio of aluminum, provided by the alumoxane, to transition metal,provided by the metallocene, of the polymerisation catalyst is between20 and 200, and for instance between 30 and 150, or preferably between30 and 100.

The details and embodiments mentioned above in connection with theprocess for manufacturing the catalyst support and the supportedcatalyst system also apply with respect to the olefin polymerisationmethod according to the present invention.

The olefin polymerisation (which includes homo- and copolymerisations)method of the present invention is preferably carried out in the liquidphase (i.e. known as “slurry phase” or “slurry process”) or in the gasphase; or in the case of propylene polymerisation also in a bulkprocess. Combinations of different processes are also applicable.

In a slurry process, the liquid comprises the olefin, either propyleneor ethylene, and where required one or more alpha-olefinic comonomerscomprising from 2 to 10 carbon atoms, in an inert diluent. The comonomermay be selected from one or more alpha-olefins such as ethylene (forexample when polymerising propylene), 1-butene, 1-hexene, 4-methyl1-pentene, 1-heptene and 1-octene. Preferably, the comonomer selected isethylene if polymerising propylene. Preferably, the comonomer selectedis 1-hexene when polymerising ethylene. In either case, the inertdiluent is preferably isobutane. Preferably, ethylene is polymerized inthe presence of a metallocene catalyst system according to the inventionin a double loop reactor, i.e. two slurry loop reactors connected inseries. In this case, an increase of 100% activity was observedaccording to the invention in comparison with a non-titanated catalystsupport.

The polymerisation process for ethylene is typically carried out at apolymerisation temperature of from 80 to 110° C. and under a pressure ofat least 20 bars. Preferably, the temperature ranges from 85 to 110° C.and the pressure is at least 40 bars, more preferably from 40 to 42bars.

The polymerisation process for propylene is typically carried out at apolymerisation temperature of from 60 to 110° C. and under a pressure ofat least 20 bars. Preferably, the temperature ranges from 65 to 110° C.,preferably 70° to 100° C., more preferably 65 to 78° C. and the pressureis at least 40 bars, more preferably from 40 to 42 bars.

Other compounds such as a metal alkyl or hydrogen may be introduced intothe polymerisation reaction to regulate activity and polymer propertiessuch as melt flow index. In one preferred process of the presentinvention, the polymerisation or copolymerisation process is carried outin a slurry reactor, e.g. in a liquid-full loop reactor.

The catalyst system of the invention is also particularly suited for gasphase polymerisations of olefins. Gas phase polymerisations can beperformed in one or more fluidised bed or agitated bed reactors. The gasphase comprises the olefin to be polymerised, preferably ethylene orpropylene, if required one or more alpha-olefinic comonomers comprising2 to 10 carbon atoms, such as ethylene (for example when polymerisingpropylene), 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene or mixturesthereof and an inert gas such as nitrogen. Preferably, the comonomerselected is 1-hexene when polymerising ethylene. Preferably, thecomonomer selected is ethylene if polymerising propylene. In eithercase, optionally a metal alkyl can also be injected in thepolymerisation medium as well as one or more other reaction-controllingagents, for example, hydrogen. Reactor temperature can be adjusted to atemperature of from 60, 65, 70, 80, 85, 90 or 95° C. up to 100, 110, 112or 115° C. (Report 1: Technology and Economic Evaluation, Chem Systems,January 1998). Optionally a hydrocarbon diluent such as pentane,isopentane, hexane, isohexane, cyclohexane or mixtures thereof can beused if the gas phase unit is run in the so-called condensing orsuper-condensing mode.

Polypropylene can also be obtained by using the metallocene catalystsystem of the invention by polymerizing propylene in a bulk process,e.g. in a loop reactor (Spheripol®) or a continuous stirred-tank reactor(CSTR), or in a Spherizone® process i.e. a multi-zone circulatingreactor. Combinations of the above types of processes are alsoapplicable e.g. continuous stirred-tank reactor (CSTR) under bulkconditions, followed by a gas phase reactor.

Surprisingly, it was found that the supported catalyst system accordingto the invention greatly improves the catalytic activity of metallocenecatalyst systems.

In one embodiment, it was found that the catalytic activity of ametallocene catalyst system for ethylene polymerisations even increasedup to 70% by using the Ti-impregnated support according to theinvention, in comparison with a non-titanated support.

Thus, the invention also covers the polyolefin as such obtainable usingthe supported catalyst system of the invention. When the catalyst systemof the invention has a Ti content of 1 to 12 wt % based on the weight ofthe Ti-impregnated catalyst support, the polyolefin obtained therewithhas an atomic molar ratio of Ti to the transition metal M i.e. Ti/M,wherein M is selected from one or more of zirconium, hafnium andvanadium, of 0.13 to 500. When the catalyst system of the invention hasa Ti content of 1 to 10 wt % based on the weight of the titanatedsilica-containing catalyst support, the polyolefin obtained therewithpreferably has a Ti/M atomic molar ratio of 1.3 to 420. The transitionmetal M indicates that the polyolefin was obtained in the presence of atleast one metallocene. In addition, the Cl/Ti atomic molar ratio of thepolyolefin should be less than 2.5. This indicates that the polyolefinwas obtained in the absence of a Ziegler-Natta catalyst, sinceZiegler-Natta catalysts include large amounts of Cl. The presence of Tiindicates the use of a Ti containing compound to boost catalyticactivity of the metallocene.

Thus in another embodiment, the invention covers a polyolefin having aTi/M atomic molar ratio of 0.13 to 500, preferably 1.3 to 420, wherein Mis selected from one or more of zirconium, hafnium and vanadium, andpreferably a Cl/Ti atomic molar ratio of less than 2.5.

The content of Ti and M of the polyolefin are measured by inductivelycoupled plasma atomic emission spectroscopy (ICP-AES) as is known in theart. The content of Cl is measured by XRF as is known in the art. Notethat the measurements are made on the polyolefin obtained from thereactor (the fluff), prior to additivation and extrusion.

Such a Ti content allows the formation of a polyolefin using far lesscatalyst, due to the increased activity of the supported catalyst systemin the presence of Ti. As a result, the polyolefin has a lower catalyticresidue, which in turn improves its use in terms of health and safety(less catalytic residue to potentially migrate to the surface). Due tothe increased activity, the polyolefins also have lower amounts ofvolatiles, because monomer and optional comonomer are more efficientlyincorporated.

Thus the polyolefin obtained using the supported catalyst system of theinvention is particular suitable for applications requiring goodorganoleptic properties e.g. for food and drink packaging.

When polymerising ethylene, the polyethylene obtained with the catalystsystem of this invention can have a molecular weight distribution (MWD)that is represented by the dispersion index D i.e. Mw/Mn (weight averagemolecular weight/number average molecular weight, measured by GPCanalysis) of typically from 2 to 10, more typically of 3 to 8, a densitymeasured according to ISO 1183 typically from 0.920 up to 0.970 g/cm³and a melt flow index (MI₂) measured according to ISO 1133, condition D,at 190° C. and 2.16 kg typically from 0.1 to 50 g/10 min, preferably 0.1to 30 g/10 min.

When polymerising propylene, the polypropylene obtained with thecatalyst system of this invention can have a density measured accordingto ISO 1183 typically from 0.920 up to 0.970 g/cm³ and a melt flow index(MI₂) measured according to ISO 1133, condition L, at 230° C. and 2.16kg, in the range from 0.05 g/10 min to 2000 g/10 min.

The polyolefins obtained using the catalyst system of the invention canbe used in any application known to the person skilled in the art.

The following Examples are given to illustrate the invention withoutlimiting its scope.

EXAMPLES

Supported Catalyst System “Catalyst Z 1”

1. Support Modification

In a 250 mL round bottom flask conditioned under a light nitrogen flow,25 g of silica was stirred at 60 rpm and dried at 110° C. overnight. 190mL of dry hexane was then added. The suspension was cooled at 0° C. and3.2 mL of VertecBip (20:80 weight ratio of Ti(OC₄H₉)₄ to Ti(OC₃H₇)₄) wasadded dropwise to impregnate the support. The suspension was mixed for20 hours at 0° C. The solvent was removed under reduced pressure and theresulting silica was dried under a nitrogen flow at 450° C. for 4 hours.The Ti-impregnated silica had a Ti content of 2 wt %.

2. MAO Treatment

20 g of dried silica was introduced in a 500 mL round-bottomed flask.Toluene was added and the suspension was stirred at 100 rpm. MAO (30 wt.% in toluene) was dropwise added via a dropping funnel and the resultingsuspension was heated at 110° C. (reflux) for 4 hours. The amount ofadded MAO was calculated to reach the desired Al loading. After thereflux, the suspension was cooled down to room temperature and themixture was filtered through a glass frit. The recovered powder waswashed with toluene and pentane before being dried under reducedpressure overnight

3. Metallocene Treatment

In 250 mL round bottom flask, 9.8 g of the above-obtained SMAO silicawas suspended in 80 mL toluene. Then, 0.2 g ofethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride in asuspension of 20 mL of toluene was added to the suspendedsilica-containing support. The resulting suspension was stirred at 100rpm for 2 hours at room temperature. Finally, the obtained catalyst wasfiltered, washed with toluene and pentane before being dried overnight.

Supported Catalyst System “Catalyst Z 2”

1. Support Modification

In a 250 mL round bottom flask conditioned under a light nitrogen flow,25 g of silica was stirred at 60 rpm and dried at 110° C. overnight. 190mL of dry hexane was then added. The suspension was cooled at 0° C. and6.4 mL of VertecBip (20:80 weight ratio of Ti(OC₄H₉)₄ to Ti(OC₃H₇)₄) wasadded dropwise to impregnate the support. The suspension was mixed for20 hours at 0° C. The solvent was removed under reduced pressure and theresulting silica was dried under a nitrogen flow at 450° C. for 4 hours.The Ti-impregnated silica had a Ti content of 4 wt %.

2. MAO Treatment

20 g of dried silica was introduced in a 500 mL round-bottomed flask.Toluene was added and the suspension was stirred at 100 rpm. MAO (30 wt.% in toluene) was dropwise added via a dropping funnel and the resultingsuspension was heated at 110° C. (reflux) for 4 hours. The amount ofadded MAO was calculated to reach the desired Al loading. After thereflux, the suspension was cooled down to room temperature and themixture was filtered through a glass frit. The recovered powder waswashed with toluene and pentane before being dried under reducedpressure overnight

3. Metallocene Treatment

In 250 mL round bottom flask, 9.8 g of the above-obtained SMAO silicawas suspended in 80 mL toluene. Then, 0.2 g ofethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride in asuspension of 20 mL of toluene was added to the suspendedsilica-containing support. The resulting suspension was stirred at 100rpm for 2 hours at room temperature. Finally, the obtained catalyst wasfiltered, washed with toluene and pentane before being dried overnight.

“Catalyst Z1” a Ti content of 1.5 wt % Ti and a Ti/Zr atomic molar ratioof 3.07.

“Catalyst Z2” a Ti content of 3 wt % Ti and a Ti/Zr atomic molar ratioof 6.14.

The content of Cl was below the detection limit, only trace amountspresent.

The content of Ti, Zr and Cl were measured using XRF.

Supported catalyst system “Catalyst C1”

1. Support Modification

Silica support was dried under a nitrogen flow at 450° C.

2. MAO Treatment

MAO was mixed in toluene with the modified support at 110° C. Afterfiltration, the recovered powder was washed and dried overnight toobtain the MAO-modified support.

3. Metallocene Treatment

The metallocene ethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconiumdichloride was stirred with the MAO-modified support at room temperaturefor 2 hours. After filtration, the recovered powder was washed and driedovernight to obtain the supported catalyst system. No titanation wascarried out.

Polymerisations

Polymerisations of ethylene were carried out with “Catalyst Z1” and“Catalyst Z2” and compared with polymerisations of ethylene using“Catalyst C1” under the same reaction conditions.

The catalyst system was injected in a 130 mL reactor containing 75 mL ofisobutane under an ethylene pressure of 23.8 bars at 85° C. forcopolymerization with a concentration of 2.4 wt. % hexene.

FIG. 1 shows the comparison of the catalytic activity between thedifferent runs, “Catalyst C1” being the comparative example. Aspresented, the impregnation of the support according to the inventionprovides increased activities. A weight percentage of only 2 and 4 wt %of Ti increased the catalytic activity by 45% and 36% respectively,compared to the Catalyst C1.

The polyethylene obtained with “Catalyst Z1” had a Ti/Zr atomic molarratio of 3.07. The polyethylene obtained with “Catalyst Z2” had a Ti/Zratomic molar ratio of 6.14.

The content of Cl was below the detection limit as measured by XRF, onlytrace amounts present. Si content was measured using XRF as well.

The content of Ti and Zr were measured using ICP-AES.

Catalytic residues were measured as follows:

PE using CATALYST Z1 PE using CATALYST C1 (invention) (comparative)Si/ppm 286.8 403 Ti/ppm 1.86 No Ti Zr/ppm 0.78 1.1

Thus the catalytic residue in the polyethylene according to theinvention using “Catalyst Z1” was less than the polyethylene obtainedusing “Catalyst C1” indicating that titanium impregnated homogeneouslythroughout the catalyst grain greatly increased the catalytic activityof the metallocene.

Polymerisations of ethylene were carried out with “Catalyst Z 1” andcompared with polymerisations of ethylene using “Catalyst C1” on an ADL(Advanced Double Loop) process. Catalyst Z1 showed 100% higher catalystactivity in comparison to “Catalyst C1”.

The invention claimed is:
 1. A process for preparing a polyolefincomprising polymerizing an olefin in the presence of a supportedcatalyst system to form a polyolefin having an atomic molar ratio ofTi/M of from 0.13 to 500, wherein M is a transition metal selected fromone or more of zirconium, hafnium and vanadium, and an atomic molarratio of Cl/Ti of less than 2.5, wherein the supported catalyst systemis prepared by a process comprising: impregnating a silica-containingcatalyst support having a specific surface area of from 150 m²/g to 800m²/g, with a mixture of titanium compounds of the general formulaR_(n)Ti(OR′)_(m) or (RO)_(n)Ti(OR′)_(m), wherein R and R′ are the sameor different and are selected from hydrocarbyl groups containing from 1to 12 carbon and halogens, and wherein n is 0 to 4, m is 0 to 4 and m+nequals 4, to form a titanated silica-containing catalyst support havinga Ti content of at least 0.1 wt % based on the weight of theTi-impregnated catalyst support; wherein the supported catalyst systemfurther comprises an alumoxane and a metallocene, and wherein themetallocene comprises a transition metal; ii). drying the Ti-impregnatedcatalyst support prior to the addition of alumoxane and metallocene onthe Ti-impregnated catalyst support; iii). adding the alumoxane on theTi-impregnated catalyst support prior to or during the addition ofmetallocene; wherein the molar ratio of aluminum from the alumoxane totransition metal of the supported catalyst system is between 30 and 100.2. The process according to claim 1, wherein polymerization is carriedout: in a gas phase process and/or in a slurry phase process.
 3. Theprocess according to claim 1, wherein the olefin is ethylene.
 4. Theprocess according to claim 1, wherein the olefin is propylene,optionally copolymerised with an alpha-olefin comonomer having from 4 to10 carbon atoms or ethylene, wherein polymerisation is carried out in abulk process.
 5. The process according to claim 1, wherein the titanatedsilica-containing catalyst support has a Ti content of 0.1 to 60 wt %based on the weight of the Ti-impregnated catalyst support.
 6. Theprocess according to claim 1, wherein the titanated silica-containingcatalyst support has a Ti content of 0.1 to 12 wt % based on the weightof Ti-impregnated catalyst support and an atomic molar ratio Ti/M,wherein M is a transition metal selected from one or more of zirconium,hafnium and vanadium, of 0.13 to
 500. 7. The process according to claim1, wherein the titanium compounds in the mixture of titanium compoundsare selected from the group consisting of tetraalkoxides of titaniumhaving the general formula Ti(OR′)₄ wherein each R′ is the same ordifferent and is an alkyl or cycloalkyl group each having from 3 to 5carbon atoms.
 8. The process according to claim 1, wherein the titaniumcompounds in the mixture of titanium compounds comprise Ti(OC₄H₉)₄ andTi(OC₃H₇)₄, and wherein the ratio of Ti(OC₄H₉)₄ and Ti(OC₃H₇)₄ is about20/80.
 9. The process according to claim 1, wherein the alumoxane ismethylaluminoxane (MAO).
 10. The process according to claim 1, whereinthe metallocene is selected from formula (I) or (II):(Ar)₂MQ₂  (I)R″(Ar)₂MQ₂  (II) wherein the metallocenes according to formula (I) arenon-bridged metallocenes and the metallocenes according to formula (II)are bridged metallocenes; wherein said metallocene according to formula(I) or (II) has two Ar bound to M which are the same or different fromeach other; wherein Ar is an aromatic ring, group or moiety and whereineach Ar is independently selected from the group consisting ofcyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl, wherein eachof said groups may be optionally substituted with one or moresubstituents each independently selected from the group consisting ofhydrogen, halogen and a hydrocarbyl having 1 to 20 carbon atoms andwherein said hydrocarbyl optionally contains one or more atoms selectedfrom the group comprising B, Si, S, O, F and P; wherein each Q isindependently selected from the group consisting of halogen; ahydrocarboxy having 1 to 20 carbon atoms; and a hydrocarbyl having 1 to20 carbon atoms and wherein said hydrocarbyl optionally contains one ormore atoms selected from the group comprising B, Si, S, O, F and P; andwherein R″ is a divalent group or moiety bridging the two Ar groups andselected from the group consisting of a C₁-C₂₀ alkylene, a germanium, asilicon, a siloxane, an alkylphosphine and an amine, and wherein said R″is optionally substituted with one or more substituents eachindependently selected from the group comprising a hydrocarbyl having 1to 20 carbon atoms and wherein said hydrocarbyl optionally contains oneor more atoms selected from the group comprising B, Si, S, O, F and P.11. The process according to claim 10, wherein each Ar is selectedindependently from an indenyl or a tetrahydroindenyl.
 12. The processaccording to claim 1, wherein the alumoxane is an oligomeric, linear orcyclic alumoxane selected fromR—(Al(R)—O)_(x)—AlR₂  (III) for oligomeric, linear alumoxanes; or(—Al(R)—O—)_(y)  (IV) for oligomeric, cyclic alumoxanes wherein x is1-40; wherein y is 3-40; and wherein each R is independently selectedfrom a C₁-C₈ alkyl.
 13. The process according to claim 1, wherein thetitanium compounds in the mixture of titanium compounds are selectedfrom the group consisting of tetraalkoxides of titanium having thegeneral formula Ti(OR′)₄; wherein each R′ is the same or different,wherein each R′ is an alkyl group having from 3 to 5 carbon atoms, acycloalkyl group having from 3 to 5 carbon atoms, or mixtures thereof;wherein the impregnation of the support by the mixture of titaniumcompounds is performed by introducing the mixture of titanium compoundsin the form of a suspension in a diluent, or by introducing the mixtureof titanium compounds dissolved in an aqueous solvent.
 14. The processaccording to claim 1, wherein the mixture of titanium compoundscomprises Ti(OC₄H₉)₄ or Ti(OC₃H₇)₄.
 15. The process according to claim1, wherein the titanium compounds in the mixture of titanium compoundsare of the general formula R_(n)Ti(OR′)_(m), wherein R and R′ are thesame or different and are selected from hydrocarbyl groups containingfrom 1 to 12 carbon and halogens, and wherein n is 0 to 4, m is 0 to 4and m+n equals
 4. 16. The process according to claim 1, wherein thetitanium compounds in the mixture of titanium compounds are of thegeneral formula (RO)_(n)Ti(OR′)_(m), wherein R and R′ are the same ordifferent and are selected from hydrocarbyl groups containing from 1 to12 carbon and halogens, and wherein n is 0 to 4, m is 0 to 4 and m+nequals
 4. 17. The process according to claim 1, wherein impregnation ofthe silica-containing catalyst support with the mixture of titaniumcompounds forms Si—O—Ti—OH on a surface of pores within thesilica-containing catalyst support prior to addition of the alumoxane tothe Ti-impregnated catalyst support.
 18. The process according to claim17, wherein drying the Ti-impregnated catalyst support prior to theaddition of alumoxane and metallocene on the Ti-impregnated catalystsupport comprises heating the Ti-impregnated catalyst support to atemperature of at least 100° C. in an atmosphere of dry and inert gas,air, or combinations thereof.
 19. The process according to claim 1,wherein adding the alumoxane to the Ti-impregnated catalyst supportcomprises mixing the alumoxane in an inert diluent or solvent with theTi-impregnated catalyst support, wherein deposition of the alumoxane onthe Ti-impregnated catalyst support occurs at a temperature between 60°C. and 120° C.
 20. The process of according to claim 1, wherein thealumoxane is added on the Ti-impregnated catalyst support prior toaddition of metallocene, and wherein adding the metallocene to theTi-impregnated catalyst support comprises mixing the metallocene withthe Ti-impregnated catalyst support.
 21. The process according to claim1, wherein the mixture of titanium compounds is a mixture of alkyltitanates.
 22. The process according to claim 1, wherein theimpregnation of the support by the mixture of titanium compounds isperformed by introducing the mixture of titanium compounds in the formof a suspension in a diluent.
 23. The process according to claim 1,wherein the impregnation of the support by the mixture of titaniumcompounds is performed by introducing the mixture of titanium compoundsdissolved in an aqueous solvent.
 24. The process according to claim 1,wherein the metallocene is selected from the group consisting ofbis(cyclopentadienyl) zirconium dichloride, bis(tetrahydroindenyl)zirconium dichloride, bis(indenyl) zirconium dichloride, andbis(1-methyl-3-butyl-cyclopentadienyl)zirconium dichloride.
 25. Theprocess according to claim 1, wherein the metallocene is selected fromthe group consisting of ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, ethylenebis(1-indenyl) zirconium dichloride,dimethylsilylene bis(2-methyl-4-phenyl-inden-1-yl) zirconium dichloride,dimethylsilylene bis(2-methyl-1H-cyclopenta[a]naphthalen-3-yl) zirconiumdichloride, cyclohexylmethylsilylenebis[4-(4-tert-butylphenyl)-2-methyl-inden-1-yl] zirconium dichloride,and dimethylsilylenebis[4-(4-tert-butylphenyl)-2-(cyclohexylmethyl)inden-1-yl] zirconiumdichloride.
 26. The process according to claim 25, wherein themetallocene is ethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconiumdichloride.
 27. The process according to claim 1, wherein themetallocene is diphenylmethylene (3-t-butyl-5-methyl-cyclopentadienyl)(4,6-di-t-butyl-fluorenyl) zirconium dichloride,di-p-chlorophenylmethylene (3-t-butyl-5-methyl-cyclopentadienyl)(4,6-di-t-butyl-fluorenyl) zirconium dichloride, diphenylmethylene(cyclopentadienyl)(fluoren-9-yl) zirconium dichloride, dimethylmethylene(cyclopentadienyl)(2,7-ditert-butyl-fluoren-9-yl) zirconium dichloride,dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](fluoren-9-yl) zirconiumdichloride, diphenylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](2,7-di-tert-butyl-fluoren-9-yl) zirconium dichloride, dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](3,6-di-tert-butyl-fluoren-9-yl) zirconium dichloride dimethylmethylene(cyclopentadienyl)(fluoren-9-yl)zirconium dichloride ordibenzylmethylene(2,7-diphenyl-3,6-di-tert-butyl-fluoren-9-yl)(cyclopentadienyl)zirconiumdichloride.